ci: upload coverage to codecov (#65)

Adds the codecov upload step right after the existing
coverage.xml artifact upload. Same pattern as attune-ai
(codecov-action v6.0.1, fail_ci_if_error: false, token via env).

Requires CODECOV_TOKEN to be set as a GitHub Actions secret
on this repo BEFORE merging — without it, codecov-action 6.0.1
rejects uploads to protected branches with HTTP 400. The
workflow stays green either way (fail_ci_if_error: false), but
the codecov reports won't populate until the secret is in place.

Author: silversurfer562

.github/workflows/tests.yml

@@ -61,6 +61,16 @@ jobs:
           name: coverage-attune-gui
           path: coverage.xml
 
+      - name: Upload coverage to Codecov
+        if: matrix.python-version == '3.11'
+        uses: codecov/codecov-action@e79a6962e0d4c0c17b229090214935d2e33f8354 # v6.0.1
+        with:
+          files: ./coverage.xml
+          fail_ci_if_error: false
+          verbose: true
+        env:
+          CODECOV_TOKEN: ${{ secrets.CODECOV_TOKEN }}
+
   frontend:
     name: frontend (Vitest)
     runs-on: ubuntu-latest